(a) Field of the Invention
The present invention relates to sheet feeder for transferring a rectangular sheet and, more particularly, to a sheet feeder for feeding a plurality of sheets, such as mail cards and envelopes, having different sizes, weights and shapes. The present invention also relates to a method for feeding a plurality of sheets one by one.
(b) Description of the Related Art
A sheet feeder for feeding a plurality of sheets thereof separately one by one in an upright posture thereof is generally used in a mail office for handling a large number of mail cards and mail envelopes.
FIG. 1 is a top plan view of a conventional sheet feeder. The sheet feeder includes a mounting table 41 for mounting thereon a plurality of sheets in an upright posture thereof, a transfer section 42 for transferring the sheets on top of the mounting table 41, and a take-out section 46 for taking out the sheets, transferred by the transfer section 42, one by one separately. The transfer section 42 includes a guide plate 43 for aligning and guiding the one of the side edges of the sheets, a bottom belt 44 for transferring the sheets in the direction perpendicular to the surfaces of the sheets while supporting the bottom edges of the sheets, and a plurality of compartments 45 for separating the sheets from one another. The take-out section 46 includes a vacuum chamber 47 maintained at a vacuum, and a suction belt 48 having a plurality of openings 50 communicated with the vacuum chamber 47 for suction of the sheet one by one. The suction belts 48 transfers the sheets around the vacuum chamber 47 while attaching the sheet to the suction belt 48 by the openings 50. A take-out belt 49 is disposed below the take-out section 46 for further transferring the sheets taken out by the suction belt 48. The mounting table 41, the transfer section 42 and the take-out section 46 are arranged substantially in a horizontal plane.
The sheet feeder of FIG. 1 operates as follows. First, the sheets mounted on the mounting table 41 at an upright posture thereof are separated from one another and applied with a thrust force at the entire rectangular surfaces thereof by the compartments 45. The sheets are transferred toward the take-out section 46 by the bottom belt 44 and the compartments 45 along the guide plate 43 in the direction of arrow A. The sheets transferred to the take-out section 46 is then subjected to suction by the suction belt 48 one by one, transferred by the revolution of the suction belt 48 around the vacuum chamber 47, and finally taken out by the take-out belt 49 in the direction of arrow B.
In the sheet feeder of FIG. 1, suppose that, as shown in FIG. 2 which is a side view taken in the direction of arrow A in FIG. 1, a mail 30 is supplied thereto having an envelope 31 with a belt wrapper 32 covering thereon for indicating the destination address of the envelope 32. In this case, there is a possibility that only the belt wrapper 32 is transferred by the suction belt 48 while leaving the envelope 31 separated from the belt wrapper 32, as shown in FIG. 3. The separation of the belt wrapper causes a problem that the mail envelope loses its destination address.